1. Field of the Invention
This invention relates to an image forming apparatus, for charging a surface of a photoconductor by a charging roller, which comprises a judging means for judging a life of the photoconductor.
2. Description of the Related Art
In an image forming apparatus which performs image forming process using a photoconductor having a photoconductive layer, it is known that deterioration of the photoconductor results in reduction of a image quality to be formed. For instance, when a surface potential of the photoconductor increases due to the deterioration, the charges can not be sufficiently canceled by an exposing process and fogs would arise in the formed image so as to provide deteriorated images only. Accordingly, it is necessary to replace the photoconductor depending on the degree of the deterioration in order to constantly obtain images of high stability and quality. Conventionally, the photoconductor has been used to be replaced when the numbers of the formed images reaches a predetermined number (e.g. approximately 40,000).
However, such manner of judging the time for replacing the photoconductor as mentioned above bases on the predetermined numbers of the formed images, irrespective of the actual used state of the photoconductor. Further, taking account of the dispersion of the individual life of the photoconductors, the threshold value of the numbers of the formed images in the counting-type photoconductor replacing method has been set to a significantly low value, taking account of the case where the life is shortest. As a result, it has been quite usual that still certainly usable photoconductors are replaced.